The present invention relates to a vibration damping mount that is used for mounting, for example, a heat shield or a housing on a member generating a vibration or heat, and relates to a metal heat shield that can be attached to, for example, an exhaust manifold of an internal combustion engine using such a vibration damping mount.
A heat shield, which is an example of such a metal exhaust manifold heat shield or housing, is used in an automobile. Such a heat shield, for example, a part near an exhaust manifold mounted on an engine of an automobile so as to control heat and sound from the exhaust manifold not to propagate to the periphery of the engine. Such a heat shield is attached to the exhaust manifold by a screw member such as a bolt.
FIG. 2 is a front view of an engine 1 of a vehicle such as an automobile showing a basic structure of this conventional technique. FIG. 40 is a sectional view of the conventional technique. The conventional technique will be hereinafter explained with reference to both FIGS. 2 and 40. An exhaust manifold 2 is attached to a side of the engine 1 in order to discharge a combustion exhaust gas. A heat shield 3 is attached to the exhaust manifold 2 so as to cover this exhaust manifold 2.
The heat shield 3 is mounted in order to control heat and sound, which is generated from the exhaust manifold 2 as a pulsating combustion exhaust gas passes through the inside of the exhaust manifold 2, not to propagate to the periphery of the engine 1. Consequently, as shown in FIG. 40, the heat shield 3 has a structure in which a damping member 6 having heat insulating properties is nipped by an inner 4 and an outer 5 consisting of a metal plate, respectively. As this damping member 6, an inorganic fibrous material or an inorganic porous material is used.
A structure for attaching such a heat shield 3 to the exhaust manifold 2 will be explained as follows with reference to FIG. 40. In the heat shield 3, an insertion hole 8 for inserting a bolt 7 is formed, and a disk-like washer 9 is arranged. The bolt 7 is inserted through the washer 9 and the heat shield 3 and screwed to an attachment boss 10 of the exhaust manifold 2. Consequently, the heat shield 3 is attached to the exhaust manifold 2.
As an example of the heat shield 3 of the above-mentioned conventional technique, an heat shield disclosed in a published document JP-A-10-266850 is known. The heat shield of JP-A-10-266850 is constituted by placing two steel sheets one on top of the other.
The heat shield with such a structure is heavy, and a momentum of a vibration of the heat shield due to a vibration, which is transmitted from an exhaust manifold via a bolt or the like, increases. Consequently, a problem occurs in that a crack tends to be caused in a portion where the heat shield is attached to the bolt or the like, and durability is deteriorated.
In addition, in the case in which it is attempted to improve a sound insulation performance in such an heat shield, it is possible that a plate thickness is increased to control a degree of transmission of noise in the heat shield. However, in this case, a weight increases as described above. Therefore, there is a problem in that it is difficult to improve the sound insulation performance with such a conventional technique.
Further, the conventional technique has problems as described below. In the case in which the heat shield 3 is attached to the exhaust manifold 2 as shown in FIG. 40, concerning a vibration that is generated from the exhaust manifold 2 and transmitted through the bolt 7, it is difficult to absorb a vibration component in a direction crossing an axis of the bolt 7 indicated by arrow A3 in FIG. 40. Due to propagation of such a vibration component, the heat shield 3 produces resonance, or metal fatigue is caused around the portion where the bolt 7 of the heat shield 3 is attached. Consequently, problems such as an increase of noise and formation of a crack in the heat shield 3 occur, and a problem arises in a quality of the heat shield 3.
Moreover, concerning heat generated from the exhaust manifold 2, other than radiant heat from the exhaust manifold 2 to the heat shield 3, heat is transmitted to the heat shield 3 via the bolt 7.
In the heat shield 3 shown in FIG. 40, since the bolt 7 is in direct contact with the washer 9, and the washer 9 is in direct contact with the heat shield 3, the heat from the exhaust manifold 2 is easily transmitted to the heat shield 3. Consequently, temperature of the heat shield 3 rises, and the radiant heat increases to easily damage, for example, auxiliary devices, ducts, and harnesses around the engine 1 in a hood due to heat. Therefore, a problem arises in a quality as a heat shield.
As one of techniques for solving such problems, a technique shown in FIG. 41 is possible. FIG. 41 is a sectional view showing a vibration damping mount 11 that is used for attaching the heat shield 3 to the exhaust manifold or the like. A structure of the vibration damping mount 11 will be hereinafter explained.
A collar 12 is mounted in an insertion hole 8 of the heat shield 3. The collar 12 includes a cylindrical coupling section 13 and a pair of flange sections 14 and 15 that are formed integrally at both ends of the coupling section 13, respectively, and expand outwardly in a radial direction thereof. A distance between the flange sections 14 and 15 is formed larger than a thickness of the heat shield 3. Damping sheets 16 and 17, which are made of, for example, a felt-like body consisting of stainless steel fiber or an expand metal of stainless steel, are inserted between each of the flange sections 14 and 15 and the heat shield 3.
In other words, the flange sections 14 and 15 of the collar 12 nip and hold the pair of damping sheets 16 and 17 that nip the heat shield 3. The bolt 7 is inserted through the collar 12 and screwed into an attachment boss of exhaust manifold 2. Consequently, the heat shield 3 is attached to the exhaust manifold 2 via the vibration damping mount 11.
In this technique, a vibration, which has traveled from the bolt 7 to the collar 12, is transmitted to the damping sheets 16 and 17 and absorbed by compression and restoration actions in an axial direction of the bolt 7 of the damping sheets 16 and 17. Consequently, in this technique, a vibration to be transmitted from the bolt 7 to the heat shield 3 is controlled.
On the other hand, in such a technique shown in FIG. 41, the damping sheets 16 and 17 deteriorate due to secular changes and self weights thereof. Consequently, it is assumed that a problem may occur in that the compression and restoration characteristics of the damping sheets 16 and 17 are degraded and the action of controlling a vibration is degraded. In addition, since the damping sheets 16 and 17 are formed of the inorganic fiber, the expand metal, or the like, it is assumed that a problem may occur in that the fiber decomposes and flies as time elapses. In these regards, it is considered that the technique shown in FIG. 41 has a problem in that a quality with respect to a vibration damping action is low.
Moreover, as a yet another conventional technique for solving these problems, a vibration damping mount disclosed in, for example, a published document JP-A-2002-235800 is known. FIG. 42 is a sectional view of a vibration damping mount 11b that is disclosed JP-A-2002-235800. The vibration damping mount 11b of the conventional technique will be hereinafter explained with reference to FIG. 42. Components in FIG. 42 corresponding to the components, which have already been explained, will be denoted by the identical reference numerals and signs and will not be explained anew.
The vibration damping mount 11b includes: a substantially annular damping member 18 formed of stainless steel or the like that is provided externally surrounding the bolt 7; and a grommet 20 formed of aluminum alloy and having substantially an S shaped section that serves as a coupling component. The grommet 20 has an insertion hole 19 through which the bolt 7, which is screwed into the attachment boss 10 or the like of the exhaust manifold 2, is inserted.
The grommet 20 includes: a first retaining section 20a having a shape with an inner peripheral edge of a circular metal plate folded back to an outer peripheral portion in order to retain the heat shield 3; a second retaining section 20b having a shape with an outer peripheral edge of the circular metal plate folded back to an inner peripheral portion in order to retain the damping member 18; and a coupling section 20c that is formed bending over the first retaining section 20a and the second retaining section 20b and couples the heat shield 3 and the damping member 18 via the first retaining section 20a and the second retaining section 20b. In addition, the collar 12 formed of a galvanized steel plate is provided between an inner periphery of the damping member 18 and the bolt 7. Gaps are provided in an axial direction and a radial direction of the bolt 7 between the collar 12 and the damping member 18.
In the vibration damping mount 11b having such a structure, a vibration, which is generated from the exhaust manifold 2 and travels through the bolt 7, is transmitted to the heat shield 3 via the damping member 18 and the grommet 20. This vibration is attenuated by actions of the damping member 18 and the grommet 20.
However, such conventional techniques have problems to be explained below. It is known that the attachment boss 10, to which the bolt 7 is attached, is often formed in a size overlapping the grommet 20 as indicated by an alternate long and two short dash lines in FIG. 42. In such a case, since the grommet 20 and the attachment boss 10 are in contact with each other, noise due to this contact increases. In addition, it is assumed that contact portions of the grommet 20 and the attachment boss 10 wear with time due to this contact to result in breakage. Consequently, a problem arises in a quality of the vibration damping mount 11b. 
In addition, on the basis of a difference of the materials of the collar 12, the damping member 18, and the grommet 20, a electrical current due to a difference of ionization tendencies of aluminum and stainless steel is generated between aluminum on a surface of the grommet 20 and stainless steel of the damping member 18, and electrolysis may occur in the grommet 20 and the damping member 18. Consequently, it is likely that the grommet 20 and the damping member 18 are broken. As a result, again, a problem arises in the quality of the vibration damping mount 11b. 